1. Technical Field
The present invention relates to a liquid feed pump and a circulation pump that pump a liquid.
2. Related Art
A liquid feed pump is known that repeats the operation of increasing the volume of a pump chamber to suck a liquid, and decreasing the volume of the pump chamber to pump the liquid. In a small liquid feed pump, a small piezoelectric element that can generate a large force as an actuator for increasing and decreasing the volume of the pump chamber is frequently used (JP-A-2011-103930 or the like).
However, the liquid feed pump that increases and decreases the volume of the pump chamber has the following problems. First, if bubbles are mixed in the pump chamber, the bubbles are crushed even if the volume of the pump chamber is decreased. Thus, the liquid within the pump chamber cannot be pressurized, and the liquid cannot be fed. If gas, such as the air, is dissolved in a liquid to be fed, the compressibility of the liquid becomes higher. Thus, the pressure within the pump chamber when the volume of the pump chamber is decreased does not rise sufficiently, and the pumping pressure of the liquid drops. In order to avoid this, it is desirable to monitor the dissolved amount (dissolved gas amount) of the air or other gases dissolved in the liquid, but it is not easy to measure the dissolved gas amount. In addition, in a case where a channel for the liquid fed from the liquid feed pump is connected to the suction side of the liquid feed pump so as to form a circulation channel system (circulation device), the liquid fed to the liquid feed pump flows through a sealed channel. Thus, it is difficult to ascertain a liquid feed amount unless a flow rate sensor or the like is separately provided.